This invention relates to a double Cardan universal joint and more particularly to an annular insert for use with double Cardan universal joints.
Conventional double Cardan universal joints provide constant driving torque transmission and are employed for driving construction vehicles or motor cars at low speeds. These universal joints can not operate satisfactorily at high speeds over 4000 rpm. The reason for this is that a centering assembly of the double Cardan universal joint for providing constant speed torque transmission is subject to seizure. In addition, these double Cardan universal joints are required to be applied with lubricant at short intervals even in the case of low speed operation.
Various types of shoe member have hitherto been proposed for receiving therein a ball member of the centering assembly. A shoe member formed of carbon steel by precision machining can be free of possible seizure at high speeds, but can not be subject to seizure when lubricant is exhausted to be free of oil film. These shoe members formed of carbon steel are generally formed with splits so as to render the manufacture thereof simple and facilitate fitting ball members thereinto. However, carbon steel material is hard and poorly resistant to seizure, burrs existing near the split or discrepancy in sliding surfaces tends to promote seizure at high speed operation.
In shoe members formed of sintered oilless alloy disclosed in U.S. Pat. Nos. 2,947,158 and 2,991,634, seizure can be prevented to a certain extent by oil contained in the alloy, even if lubricant leaks and exhausts from the shoe members. These shoe members each consist of a plurality of parts so as to accommodate rapping during sintering and to compensate for slight elastic deformability of the material during the assembly of a ball member. However, when a shoe member consists of a plurality of parts, a difficulty is encountered in fixing in place the shoe member in a narrow space within the centering assembly and high precision is degraded during assembling, thereby causing seizure or noise to develop.